Igniter



April 22, 1958 L. R. 1-:NT2 2,831,993

IGNITER Filed July l0, 1956 ATTORNEYS United States Patent t `Spark Plug Company, Toledo, Ohio, a corporation of Delaware Application July 10, 1956, Serial No. 596,918

3 Claims. (Cl. S13-11.5)

This invention relates to igniters for gas turbine engines or jet engines and is particularly directed to the construction of the shell portion of such an igniter.

It has heretofore been proposed to provide igniters that extend into the combustion chambers of gas turbine and jet engines with openings through which Ventilating or cooling air can be passed. Such cooling air is required to save the igniter from destruction during normal operation of the engine. Even with a large volume of cooling air passed through the igniter it is not uncommon for the temperature of the shell to reach 1800 F. since the igniter extends into the hottest part of the llame in the combustion chamber.

In starting a gas turbine or jet engine it is customary to rotate at least the compressor wheel at high velocity priorto the initial introduction of fuel so that the air flow within the engine assumes a normal, working pattern. With ventilated igniters this pattern includes the passage of air through openings on the upstream side of the igniter and down in the shell and out around the electrodes where the initial spark will occur.v Starting diiculties have been encountered with certain types of igniters in certain engines for the reason that the normal air iiow pattern and velocity is such that the air llow is suicient to blow the fuel-air mixture away from the area where the spark occurs. Under these circumstances the fuel-air mixture is, of course, not ignited.

Attempts have been made to remedy the diiiiculty by closing oli the end of the igniter and directing the air flow out at another point rather than immediately around the sparking tip. Such eiorts have not proved successful because of the great increase in the temperature atr tained by the igniter in service, resulting in a very short life.

A primary object of the present invention is to provide an igniter in which the Ventilating passage `is initially closed but which opens automatically in response to an increase in operating temperature.

Another object of the invention is to provide an igniter of the above type in which there is no change in the characteristics of the spark gap by reason of the increase in temperature which causes the Ventilating passage to open.

Other objects and advantages of the invention will become apparent from the following speciiication, reference being had to the accompanying drawing which shows a central vertical sectional view of an igniter embodying the present invention.

In the accompanying drawings:

Figure l is a longitudinal view in section of an igniter.

Figure 2 is the lower portion of the igniter shown in Fig. l.

Referring to the drawing the igniter comprises amounting flange 1 which supports an outer heat shielding shell member 2 and an inner shell member 3 which extend into the combustion chamber of the associated engine. It will be noted that the inner shell member 3 and outer shell member 2 are electrically connected immediately adjacent y "ice the flange and are thus grounded electrically to the wall of the engine, and that the outer shell 2 is fixed in position with relation to the mounting ange, its free end extending inwardly around the inner shell 3.

An insulator 4 is seated in the inner shell member 3, being held in place in any suitable manner as by a shield barrel S which is threaded into the inner shell member 3 against a suitable shoulder 6 on the insulator. A lower shoulder '7 of the insulator seats against a corresponding shoulder of the inner shell member. Below the shoulder S the inner shell member and outer shell member are spaced apart a substantial distance to provide a cylindrical passage lil through which cooling air may How.

A central electrode 1 of any suitable form is seated `in and supported by the insulator 4. At itslower end the center electrode il is electrically and physically connected to a body of semi-conductive material 12. Gas leakage around the inner and outer sides of the semi-conductive body may be prevented in any suitable manner as by introducing and tamping masses of granular material 13 and ifi in place `in a manner well known in the art.

At its lower end the semi-conductive body 12 seats on an inturned flange 16 of the inner shell 3 and the extreme inner periphery of the iiange 16 forms the ground electrode fora spark gap between the center electrode 11 across the vertical and horizontal surfaces of the semiconductive body 12.

The semi-conductive body will be eliminated in certain types of igniters, and the center electrode 11 supported in a ceramic insulator following the conventional spark plug practice.

The lower end of the cylindrical cooling air passage 10 is closed off when the igniter is cold by an inturned flange 18 formed on the lower end of the outer heat shielding shell 2. Normally the flange 1S abuts the lower and outer surface of the liange 16 of the inner shell 3 so that no air can flow through the passage 10. When the igniter is in use, however, after the engine has been started and has attained its operating temperature the thermal expansion of the shell 2 causes it to elongate to such an extent that the inturned iiange 18 moves away from the flange 16 or the lower end of the inner shell member 3, thus opening a passage for the discharge of air from the passage l@ around the lower end of the inner shell and radially inward across the end of the semiconductive body i2. The cooling effect of the air flowing rapidly through the passage 10 is suflieiently great that the inner shell 3 and the semi-conductive body 12 operate at relatively low temperatures, well within their safe limits, and have a greatly prolonged life.

it will be noted that the length and geometry of the spark gap formed between the center electrode 11 and the inturned inner shell liange 16 remains unchanged durinf' operation and that the semi-conductive body 12 is grounded to the inner shell. The inner shell and parts carrier thereby thus constitute an inner sparking member.

The path of air iiow is diagrammatically indicated in Figure l. When the engine is cold, air enters an opening Ztl in the upstream side wall of the outer shell 2, passes through the passage 10 and around the inner shell 3 and exits through an opening 23 in the downstream wall of the outer shell 2. When the engine is at operating temperature air enters the same intake passage and iiows through passage 10 in much the saine manner but exits largely through the space `between the anges 16 and 18 at the tip of the igniter. Thus the igniter tip is cooled and its life significantly prolonged. while at the same time air is prevented from flowing through the passage between the iianges 16 and 18 when the igniter is `cold and the parts contracted.

`While the igniter exhibits its most advantageous performance during starting when the passage between the assigns vantage accruesin the vevent that it is necessary to re-'start the engine after a llanieout The rapid passage of cooling air in theabsence ,of combustion in the combustion chamber causesfthe outer shell 3 to contract sig- I`n'iricantly. Even thoughthe shell may not seatfully with lits flange '18 against'the lflange le of the inner shell the opening between these'anges is so restricted that the flow'of air betvveenthem will not seriously interfere with sparking and ignition of the fuel mixture because its velocity is not st iiiciently greatto blow the fuehair minture away fromthe spark gap.

`lt has been found in vpractice that the coeicient of thermal expansion of the inner and outer shells need not be vgreatly different as would at rst he expected. it appears that the difference in normai operating ternl.peratures is such 4that the outer Vshell expands enough more than vthe inner shell so that its flange l@ leaves the'ilange 16 lot Vthe inner shell and opens a satisfactory clearancefor the passage of cooling air. Or" Course if it is Vdesiredto increase the opening for any reason, the outer shell maybe made of a material having a greater coefficient of thermal expansion, so long as the chosen material vis capable of resisting the high normal operating temperatures.

While the invention has been disclosed in conjunction with a specic form and disposition of the parts it should be expressly'understood that numerous modifications and changes may be made without departing from the scope of theappended claims.

WhatvI claim is:

l. igniter comprising an inner sparking portion having'spaced center and shell electrodes disposed at an end 'extending into an engine combustion chamber, a

heat shielding outer shell surrounding and radially spaced from said inner portion 'over the length of th'eend extending into the combustion chamber, means to fix one end of said outer shell, said outer shell having a portion in contact with said inner portion when cool and which move away from said inner portion by thermal expansion when at normal operating temperatures, and said outer shell having an opening for the admission of cooling air into the radial space between said inner portion and said outer shell.

An igniter comprising an inner sparkingportion having spaced center and shell electrodes disposed at an end extending into an engine combustion chamber, a heat shielding outer shell surrounding and radially spaced from said-inner portion over the length of the end extending into the combustion chamber, means to tix one end of said outer shell, said outer shell having a portion in Contact with said inner portion when cool and which move axially away from said inner portion by thermal expansion when at normal operating temperatures, 'and said outer shell having an opening for the admission of' cooling air into the radial space between said inner portion and said outer shell.

3. An igniter in accordance with claim 1 in Which said outer sheet has kan iaturned ange at its free end, which flange abuts said inner portion when cold and moves away from said inner portion at normal operating temperatures,

'whereby cooling air ilows around the tip of said inner portion only at normal operating temperatures.

References Cited in the file of this patent UNITED STATES PATENTS 2,609,808 Bychinsky Sept. V9, Av1952 

